The present invention relates to a process for the production of liquid fuel wherein coal is effectively liquefied. More particularly, the present invention relates to a process for efficiently liquefying coal wherein a heavy oil of petroleum series having a high carbon content is used as starting material and subjected to a heat treatment conducted at a relatively low temperature.
Coal has been used as fuel for a very long period of time from the beginning of human history. With the increasing output of petroleum in recent years, however, the position of coal as industrial and domestic energy source is being replaced by petroleum. Major reasons therefor are that coal is solid and is incovenient in storage and transport as compared with liquid petroleum, that coal contains a large amount of ashes and that coal is low in combustion efficiency.
In order to improve these shortcomings of coal, various attempts have been made to liquefy coal. The methods for liquefying coal are roughly classified into a hydrogenolyzing method and a solvent treatment method, the former comprising the treatment of coal at a high temperature with highly pressurized hydrogen for producing chiefly light oils such as gasoline and the latter comprising the steps of mixing coal with a heavy oil solvent of coal series such as creosote oil, anthracene oil and coal tar and subjecting the mixture to a heat treatment to produce heavy oils.
On the other hand, many researches have been made on effective utilization of heavy oils of petroleum series produced in a large amount as by-product with the recent increase in consumption of petroleum. One of the key problems is utilization of the heavy oils as a solvent for liquefaction of coal. However, heavy oils of petroleum series are hardly miscible with those of coal series and thus fail to exhibit satisfactory extraction efficiency. Hitherto, therefore, no success has been reported in attempts to liquefy coal with a heavy oil of petroleum series.
Afterwards, the present inventors developed a process for the production of liquid fuels of good quality which comprises incorporating powdery coal with a heavy oil of petroleum series in an amount of at least 50 parts by weight per 100 parts by weight of the powdery coal, subjecting the mixture to a heat treatment conducted at 400.degree.-450.degree. C. and thereafter removing a solid coagulated material formed in the treated product (U.S. Pat. application Ser. No. 549,360).
As this process requires a treating temperature as high as 400.degree. C. or more, however, the process involves problems to be improved in the aspects of thermal energy and operation conditions.